1. Field of the Invention
The present invention relates to a method of manufacturing semiconductor devices. More particularly, the present invention relates to a process of stripping photoresist from a semiconductor wafer using a solution of dimethylacetamide or a solution of monoethanolamine and dimethylsulfoxide.
2. Description of the Related Art
In general, the fabricating of semiconductor devices involves the use of photolithography for forming a pattern on a semiconductor wafer.
In photolithography, a photoresist deposited on the semiconductor wafer is selectively removed in a series of processing steps, such as an exposure step, a development step, etc. A pattern designed according to the desired characteristics of the semiconductor device is formed on the semiconductor wafer using the photoresist as a mask.
Photoresists can be classified into two groups: positive photoresists and negative photoresists. Whether a photoresist is considered to be of a positive type or of a negative type depends on the region thereof which is removed after selected portions of the photoresist are irradiated during the exposure process.
That is, the positive type of photoresist is one in which the exposed regions of the photoresist are removed from the semiconductor substrate. The negative type of photoresist is one in which the non-exposed regions of the photoresist are removed from the semiconductor substrate.
On the other hand, photoresists can also be classified according to the wavelength at which the photoresist responds with respect to its exposure and development. Photoresists classified in this way include those of the I-line group, the G-line group, and the Deep-UV group.
When an Hg-Arc lamp is used as the general light source in the semiconductor device manufacturing process, photoresists are classified in the I-line group, G-line and Deep-UV according to the wavelength of light from the spectrum of the Hg-Arc lamp. More specifically, a photoresist in the I-line group responds to light having a wavelength of 365 nm. A photoresist in the G-line group responds to light having a wavelength of 436 nm, and a photoresist in the Deep-UV group responds to light having a wavelength of 248 nm.
In a conventional semiconductor device fabrication process, a positive photoresist in the I-line group is normally used. That is, the regions of a photoresist exposed to light having a wavelength of 365 nm are selectively removed from the semiconductor substrate.
However, photolithography using a positive photoresist in the I-line group has its limits. In particular, such a process can only form a pattern as small as 0.3 xcexcm. Such a process, therefore, is not suitable for manufacturing the highly miniaturized semiconductor devices which are now in demand.
Accordingly, recent semiconductor device fabrication processes employ photoresists in the Deep-UV group. These photoresists can be used to form patterns smaller than even 0.2 xcexcm.
However, photoresists in the Deep-UV are inferior to those in the I-line group in terms of their resistance to light and heat. This is because the constituents of the photoresists in the I-line group and the photoresists in the Deep-UV group, such as the polymer component, the light-reactant, and the solvent, are different from each other.
In fact, photoresists in the Deep-UV group are not widely used in semiconductor device fabrication because no chemical has yet been developed which can completely remove a Deep-UV group photoresist remaining on a semiconductor substrate after the photolithography has been completed.
An object of the present invention, therefore, is to provide a semiconductor device fabrication method including a process in which a Deep-UV group photoresist can be completely removed from the semiconductor substrate.
Another object of the present invention is to provide a semiconductor device fabrication method including a process which is so flexible that it can be used to completely remove either a Deep-UV group photoresist or an I-group photoresist from a semiconductor substrate.
To achieve these and other objects and advantages, the present invention is characterized in that it uses only dimethylacetamide to strip any remaining photoresist from the semiconductor substrate after the exposure and development steps of the photolithography process are carried out.
The present inventors have found that dimethylacetamide can remove either a positive photoresist in the Deep-UV group or a positive photoresist in the I-line group. The photoresist is typically formed on a film, such as an insulating film, a metallic film, or a multilayered-film comprising an insulating layer and a metallic layer.
Preferably, the stripping process is carried out for less than 300 sec. while the dimethylacetamide is maintained at about 10xc2x0 C. to 40xc2x0 C. In addition, the stripping process is preferably carried out by spraying the dimethylacetamide onto the photoresist.
The method further comprises a step of baking the photoresist before the photoresist is exposed. The baking step is preferably carried out at a temperature below 200xc2x0 C. for less than 300 seconds.
To also achieve the above-described and other objects and advantages, another embodiment of the present invention is characterized in that it uses a mixture of monoethanolamine and dimethylsulfoxide to strip any remaining photoresist from the semiconductor substrate after the exposure and development steps of the photolithography process are carried out.
The mixture is preferably 20 to 80 weight % monoethanolamine with the remainder being the dimethylsulfoxide.
The present inventors have found out that such a mixture of monoethanolamine and dimethylsulfoxide can remove either a positive or negative photoresist in the Deep-UV group, as well as either a positive or negative photoresist in the I-line group.
The monoethanolamine and dimethylacetamide are maintained at a temperature of about 10xc2x0 C. to 40xc2x0 C. while they are sprayed on the semiconductor substrate. Preferably, the monoethanolamine and the dimethylsulfoxide are sprayed separately onto the photoresist where they mix.
In addition to the baking step mentioned above, the process also includes a step of rinsing the semiconductor substrate once the photoresist has been removed therefrom by the monoethanolamine and the dimethylsulfoxide.
The rinsing is preferably carried out for less than 120 sec. at a temperature of about 10xc2x0 C. to 40xc2x0 C. The rinsing may be carried out using deionized water or acetone.